The cause of the problem is still unknown but I suspect I didn't have the High Voltage cage correctly seated which caused the main fuse and the resistor on the safety interlock switch to blow.
However the two resistors on the parasitic choke from one of the tubes had burnt out and that would not be caused by the first issue so something else was certainly not right. I ordered some new resistors and carefully replaced the damaged items but replacing the two resistors on the choke with just one, (no idea why there had been two in the first place, maybe the previous owner could not find the right value), followed by a good clean out and then lubricating all the switches. This is the first time I've delved in to the old amplifier and everything was a bit unknown, but I must thank the guys at QRZ.com and my local club CARA who gave advice and help which was extremely useful in the fault finding.
The repaired parasitic resistor all soldered up and ready to be refitted.
Just as important I have learn't a lot about the old valve amplifiers and saved myself a ton of money which can only be a good thing!
More testing to follow so I shall keep you updated.